Blood purifier

The invention discloses a blood purifier. The blood purifier comprises an artery pipe, a vein pipe and a blood filter. The artery pipe communicates with an artery kettle after bypassing a blood pump, and the vein pipe communicates with a vein kettle. A displacement liquid communicates with the vein kettle after bypassing a displacement liquid pump through pipes. A liquid waste output port of the blood filter communicates with a liquid waste collecting bag after bypassing a liquid waste pump through pipes. One in-film joint of the blood filter communicates with a first multi-pipe gating switch, and the other in-film joint of the blood filter communicates with a second multi-pipe gating switch. The first multi-pipe gating switch communicates with the vein kettle, and the second multi-pipe gating switch communicates with the artery kettle. Both the first multi-pipe gating switch and the second multi-pipe gating switch have ports connected with a blood filter to be replaced. The blood purifier can solve the problems, such as blood exosmosis, increase of financial burden for a patient caused by frequently whole pipe replacement, influence on blood filtration, and increase of risk of blood infection, caused by direct separation of cruor in pipes during blood purification and installation of pipes and a blood filter.